This invention relates to a coupling for connecting a drop box having a hook located at its front end to the endless chain of a roll off hoist.
There currently are two general systems for loading drop boxes onto a truck for transportation and then unloading them again upon arrival at the intended destination. One of these systems uses a cable having a loop at its end which fits over a hook located at the front of the drop box. The cable is wound onto a winch to pull the drop box up a tilting frame located on the truck. With this system the drop box is unloaded by backing the truck toward the intended drop point and stopping it abruptly. Inertia then causes the drop box to slide off of the truck.
A more recent system improves upon the winch feed system by providing an endless chain in the tilting frame which can be moved in either direction. A carriage, which is connected to the chain, rides on a track located on the frame. The carriage has a hook located on it which is arranged to engage a horizontal bar located on a tongue at the front of the drop box. With this system the carriage can be coupled to the drop box automatically by running the carriage to the bottom of the frame, backing the truck towards the bin so that it is adjacent to the tongue and then moving the carriage back up the track.
Not only can the drop box be coupled to the lifting device automatically with this system, but the chain can be used to positively push the drop box off the truck when it is time to unload it. This allows more precise placement of the drop box and even allows unloading the drop box onto a dock having the same height as the truck.
Because the endless chain system is superior to the cable system, many users of the latter are changing to the former. However, heretofore doing so required conversion of each drop box from one having a hook to one having a horizontal bar which can be engaged by the hook on the chain. Otherwise, it would be necessary to manually interconnect the hook on the chain with the hook on the drop box, with a short piece of cable for example. Conversion is expensive, particularly when a large number of drop boxes are involved and manually coupling is inefficient. What is needed, therefore, is a coupling device on an endless chain type of roll off hoist which automatically will engage the hook of a cable type drop box.
This is accomplished in the present invention by providing a pivot plate which is rotatably mounted on the carriage and which is attached to the chain. The chain is connected to the side of the pivot plate which faces the extremity of the frame at a location below the axis that the pivot plate connects to the carriage and to the other side of the pivot plate at a location above this axis. Mounted on top of the pivot plate is a U-shaped bail which is arranged to engage the hook on the bin. A stop, which is located on the track which the carriage runs on, prevents the carriage from moving past a certain point toward the extremity of the frame. Thus, when the carriage contacts the stop further movement of the chain toward the extremity causes the pivot plate, and thus the bail, to rotate upwardly. When the direction of the motor is reversed, the pivot plate and bail then drop back to their original positions.
In operation, a bin is loaded by tilting the frame from its horizontal traveling position to an angled position where its extremity is proximate the ground. The carriage then is driven up against the stop thereby raising the tip of the bail. When the bail is lifted the truck is backed toward the drop box until the bail is located over the hook and the carriage is moved back up the track. As the carriage pulls away from the stop the bail drops over the hook and engages it. Further movement of the carriage causes the drop box to be pulled up onto the frame and the frame is then rotated to its horizontal position. In unloading the drop box the chain merely is moved towards the extremity of the frame. A pusher plate located on the carriage contacts the drop box and pushes it off of the truck.
Accordingly, it is a principal object of the present invention to provide a coupling for interconnecting a drop box having a loading hook to the carriage of an endless chain roll off hoist.
It is a further object of the present invention to provide such a coupling which engages the hook automatically upon movement of the carriage along the frame which supports it.
The foregoing and other objectives, features and advantages of the present invention will be more readily understood upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings.